THE UNKNOWN UNSUBSTITUTED TETRAZINES - 1,2,3,4-TETRAZINE AND 1,2,3,5-TETRAZINE

Ab initio theoretical methods have been used to determine the equilibrium geometry of the unsubstituted 1,2,3,4- and 1,2,3,5-tetrazines. Double zeta (DZ) and double zeta plus polarization (DZP) basis sets have been used at both the self-consistent field (SCF) and single and double excitation configuration interaction (CISD) levels of theory. Harmonic vibrational frequencies and infrared intensities have been evaluated at the SCF level of theory. Comparisons between these and previous results at the SCF level using smaller basis sets have been made. The 1,2,3,5-tetrazine is predicted to lie 8 kcal mol-1 below the experimentally characterized s-tetrazine (i.e., 1,2,4,5-tetrazine). The work strongly suggests renewed experimental efforts toward the laboratory identification of 1,2,3,5-tetrazine.